The permanent alteration of the color of keratinous fibers, in particular human hair, by the application of hair dyes is well known. Oxidative hair dye precursors, i.e., developers (also called primary intermediates) and couplers diffuse into the hair through the cuticle and into the cortex. The precursors combine in the presence of an oxidizing agent, such as hydrogen peroxide, to form larger-sized dye molecules that result in a visual color of the hair (“end hair color”). Different combinations of developers and couplers produce different shades of hair color when combined with the oxidizing agent. The end hair color is not easily predicted given the complex chemical process that occurs to achieve an end hair color.
Permanent hair colorant formulations should produce end hair colors that are stable for at least 4 to 6 weeks. Additionally, the end hair color should exhibit good washfastness, good lightfastness, fastness to rubbing, as well as sufficient resistance with respect to perspiration. Preferably, it should be possible to produce a broad palette of different color shades by combining suitable developers and couplers.
Hair colorant formulations generally provide acceptable and immediate results. However, achieving both desired shade (hue) and depth of shade (chroma) remains challenging, particularly for hair colorant formulations that impart bright violet colors to the hair. To achieve desirable shades in the bright violet area, the combination of 1,4-diaminobenzene compounds with 2,6-dihydroxyethylaminotoluene compounds has been used. Nevertheless, the bright violet shades may fail to provide the desirable red hue and chroma and, thereby, the hair colorant formulation may fall short of producing the desired end hair color.
U.S. Pat. No. 5,230,710 discusses a class of 2,6-diaminotoluene based couplers having formula (A):
in which R and R1 of formula (A) are independent from each other and are represent hydrogen, lower alkyl or hydroxyalkyl, acyl, of an N-alkylated or unsubstituted amino lower alkyl or carbamylmethyl group. The combination of 2,6 diaminotoluene based couplers is described in combination with 1,4 diaminobenzenes compounds such as p-phenylenediamine, p-toluoylenediamine, N,N-dimethyl-p-phenylenediamine, chloro-p-phenylenediamine and methoxy-p-phenylenediamine.
There remains an ongoing need for additional hair colorant compositions that can provide desirable bright-violet shades, particularly when used with various oxidant systems, i.e., ammonium carbonate, hydrogen peroxide, and, optionally, a radical scavenger and/or chelant.